1. Field of the Invention
The present invention relates to the field of fabrication of integrated circuits, and more particularly, to a process tool used for the chemical mechanical polishing of substrates during the fabrication of integrated circuits.
2. Description of the Related Art
In modern integrated circuits, a huge number of semiconductor elements, such as field effect transistors, capacitors and the like, are fabricated on a single substrate. These individual semiconductor elements have to be connected to each other via so-called metallization according to the required functionality of the integrated circuit. To this end, a so-called interlayer dielectric is deposited above the devices, and vias and trenches are formed thereafter in the dielectric layer. The vias and trenches are then filled with an appropriate metal, for instance copper in sophisticated integrated circuits, to provide for the electrical connection of the individual semiconductor elements. Due to the ever-increasing number of semiconductor elements and the immense complexity of modern integrated circuits, typically a plurality of metallization layers must be stacked on top of each other to accomplish the functionality required.
As the number of metallization layers and, associated therewith, the number of dielectric layers to be stacked on top of each other have increased, the planarization of the individual stack layers at each process level has been found to represent an extremely critical manufacturing process. This problem is additionally exacerbated as the substrate area, i.e., the wafer diameter, is steadily increasing. Chemical mechanical polishing (CMP) is an appropriate and widely used process to achieve global planarization of a wafer. In the CMP process, a wafer is mounted on an appropriately formed carrier, a so-called polishing head, and the carrier is moved relative to a polishing pad while the wafer is in contact with the polishing pad. A slurry is supplied to the polishing pad during the CMP process and contains a chemical compound reacting with the material or materials of the layer to be planarized by, for example, converting the material into an oxide, and the reaction product, such as the metal oxide, is mechanically removed with abrasives contained in the slurry and the polishing pad. To obtain a required removal rate, while at the same time achieving a high degree of planarity of the layer, a combination of polishing pad, type of slurry, pressure applied to the wafer while moving relative to the polishing pad, and the relative velocity between the wafer and the polishing pad must appropriately be selected. The removal rate further significantly depends on the temperature of the slurry, which in turn is significantly affected by the amount of friction created by the relative motion of the polishing pad and the wafer, the degree of saturation of the slurry with ablated particles and, in particular, the state of the polishing surface of the polishing pad.
Most polishing pads are formed of a cellular microstructure polymer material having numerous voids which are filled by the slurry during operation. A densification of the slurry within the voids occurs due to the absorbed particles that have been removed from the substrate surface and accumulated in the slurry. As a consequence, the removal rate steadily decreases, thereby disadvantageously affecting the reliability of the planarizing process and thus reducing yield and reliability of the completed semiconductor devices.
To partly overcome this problem, typically a so-called pad conditioner is used that xe2x80x9creconditionsxe2x80x9d the polishing surface of the polishing pad. The pad conditioner may be comprised of a variety of materials, e.g., diamond that is covered in a resistant material. In such cases, the exhausted surface of the pad is ablated and/or reworked by the relatively hard material of the pad conditioner once the removal rate is assessed to be too low. In other cases, as in sophisticated CMP apparatuses, the pad conditioner is continuously in contact with the polishing pad while the substrate is polished. Whereas the first alternative leads to significant variations of the removal rate due to the difference of the reworked surface of the polishing pad compared to the exhausted surface present immediately before the conditioning, the latter alternative is not as effective as the former alternative in refreshing the pad surface, since a substantially softer conditioning material has to be used in order to not unduly shorten the lifetime of the polishing pad. Moreover, in sophisticated integrated circuits, process requirements concerning uniformity of the CMP process are very strict so that the state of the polishing pad has to be maintained as constant as possible over the entire area of a single substrate as well as for the processing of as many substrates as possible. Consequently, the pad conditioners are usually provided with a drive assembly and a control unit that allow the pad conditioner to be moved with respect to the polishing head to rework the polishing pad immediately before coming into contact with the substrate to be processed while avoiding interference with the movement of the polishing head. This additionally adds to the costs and complexity of presently known CMP apparatuses.
In view of the above-mentioned problems, there exists a need for an improved CMP tool allowing for a stable operation over a large plurality of substrates to be treated.
In general, the present invention is directed to a CMP tool having conditioners integrally formed with the polishing head to reduce cost and complexity of the tool while improving effectiveness and reliability.
According to one embodiment of the present invention, a polishing head for the chemical mechanical polishing of a substrate comprises a substrate holder configured to receive the substrate and to hold it in place during operation. The polishing head further comprises a joining element connectable to a drive assembly for moving the polishing head and a supply line that is connectable to a vacuum source and/or a gas source. Moreover, the polishing head comprises a pad conditioner coupled to the substrate holder.
According to a further embodiment, a polishing head for the chemical mechanical polishing of a substrate comprises a substrate holder configured to receive the substrate. Moreover, the polishing head includes a retaining element arranged to enclose the substrate and to keep it in place during operation of the polishing head, wherein the retaining element includes a conditioning surface.
In a further embodiment, an apparatus for the chemical mechanical polishing of a substrate comprises a polishing pad and a polishing head having formed therein a pad conditioning surface. Moreover, the apparatus includes the drive assembly for moving the polishing head relative to the polishing pad.
Pursuant to a further embodiment, an apparatus for the chemical mechanical polishing of a substrate comprises a polishing head for receiving, holding and moving the substrate.
The apparatus further comprises a polishing pad and a pad conditioner that is mechanically connected to the polishing head.
In a further embodiment, a polishing tool for a chemical mechanical polishing tool comprises a substrate holder configured to receive a substrate and a pad conditioner coupled to the substrate holder.